1. Field of the Invention
The present invention relates to an integrated circuit and a circuit board for connecting analog input/output lines to the circuit board side by solder connection of leadless terminals, and in particular, relates to an integrated circuit and a circuit board for self-diagnosing failure of signal lines including leadless terminals which externally connect analog input/output lines caused by manufacturing defects.
2. Description of the Related Arts
Conventionally, downsizing of parts and high density mounting are underway for electronic devices such as information processing devices, in order to realize requirements for downsizing the devices and for high-speed signal transmission. In order to realize such high-density mounting, elaborated structures are used for packages of integrated circuits. Conventionally, ball grid arrays (Ball Grid Array) and QFN packages (Quad Flat Non-Leaded Package) are known as leadless package structures which are suitable for high-density mounting of integrated circuits. A ball grid array, so-called BGA, is a package in which leadless terminals composed of solder balls are arranged in a grid with predetermined gaps therebetween on the bottom surface of the package which is in contact with a printed board, and the leadless terminals are soldered on the corresponding pattern of the printed board. Since the leadless terminals are on the bottom side of the package and in the narrow space sandwiched between the package and the printed board, solder paste for joining is applied in advance on the pattern of the printed board in a printing process, and the entire package is heated so as to perform soldering by melting the solder for joining which is in contact with the terminal part. Meanwhile, the QFN package is a package having a structure in which leads are removed and merely electrode pads for soldering are formed, wherein the electrode pads are positioned on the bottom surface of the package.
If failure of decreasing operating margins is present in a circuit device on which an integrated circuit using the ball grid array or QFN is used as a package structure, particularly, in an analog circuit part of a motor rotation speed control loop including a PLL, i.e., a charge pump circuit or the circuit part of a loop filter; a feedback loop is formed, therefore, the rotation control thereof can be generally performed. However, the rotation variation and rotation speed do not always satisfy specifications. In a method for narrowing down the failure location in such a case, the loop is opened so as to precisely measure and examine gains and linearity of operations of each block and operation points (offset); however, since normal operations cannot be performed when the loop is opened, specifying the location of the cause is extremely difficult, and requires advanced skills and many man-hours. When the location of failure is to be found out, it is required to see the state of the leadless terminals on the package bottom surface from which analog output signals are output to the circuit of the circuit board side; however, since the terminal part is hidden behind the package, it is difficult to detect short circuit failure, etc., which is due to abnormality in soldering part, poor connection, or adhesion of foreign conductive substance, by appearance examination by means of visual observation, therefore, obstacles for specifying the location of failure are caused. According to the present invention to provide an integrated circuit and a circuit board capable of readily diagnosing failure which is due to the terminal state of the integrated circuit having a package structure in which analog input/output lines are soldered on the circuit board side by leadless terminals which cannot be seen or difficult to be seen from outside in a mounted state.